You Must Know
1. Electricity now has a very important role in our day-to-day life.
2. An electric cell is a source of electricity. It has two terminals, a positive terminal and a negative terminal.
3. An electric bulb, or lamp, is a device that produces light from electricity. It has two terminals, and a filament contained in a glass bulb (filled with an inert gas).
4. An electric torch has three main parts; a bulb, a cell/battery and a switch. On ‘closing the switch’ an electric current flows from the cell to the bulb. This heats. up the bulb and it starts glowing.
5. An electric circuit is a closed and complete path in which an electric current can flow.
6. The three essential components of an electric circuit are: (i) an electric cell/ battery, (ii) connecting wires and (iii) an electric switch. We also have a device (like the bulb/lamp) through which the current flows.
7. Electric switch is an electric component that can ‘break’ or ‘make’ (complete) an electric circuit as per our requirement.
8. An electric bulb glows only when it is in a complete closed circuit.
9. Conductors are those objects, or materials, which (easily) allow electricity to pass through them.
10. Insulators are those objects, or materials, which do not allow electricity to pass through them.
11. Electric wires are covered with insulators to avoid/prevent electric shocks.
12. One should always use rubber gloves and/or rubber sandals while handling/ adjusting electrical appliances/devices.
Something To Know
A. Fill in the blanks.
1. The thin coiled wire, that gives light, when heated up, is known as the filament of an electric bulb.
2. An electrical device needs at least two terminals.
3. An electric bulb glows when a current flows through it.
4. The device, that is used to ‘break’ or ‘make’ an electric circuit, is called an electric switch.
5. The materials, which (easily) let electricity flow through them, are called conductors.
6. Electric current does not pass through a sheet of plastic.
B. Write True or False for the following statements.
1. A dry cell stops working when the chemicals in it get used up. True
2. Electric current is taken to flow from the negative terminal of the (electric) cell to the positive terminal of the cell. False
3. We need to complete the relevant electric circuit to enable an electric device to work. True
4. Button cells are used in wrist watches. True
5. We can use a polyester thread, in place of metal wires, to complete an electrical circuit. False
C. Tick (✔) the correct option.
1. The thin metal wire inside a electric bulb, is known as-
insulation
terminal
filament
fiber
Answer – filament
2. When an electric current start flowing in an electric bulb, it starts emitting light because its—
filament starts emitting light and then gets heated up.
thick connecting wires start emitting light and then get heated up.
filament gets heated up and then starts emitting light.
thick wires get heated up and then start emitting light.
Answer – filament gets heated up and then starts emitting light.
3.The basic electric circuit needs to have-
only a source of electric current.
only a few conducting wires.
only an electric switch.
a source of electric current, a few conducting wires as well as an electric switch.
Answer – a source of electric current, a few conducting wires as well as an electric switch.
4. The electric bulb, in the circuit shown. here, would glow when-
both switches 1 and 2 are in their ‘OFF’ positions.
switch 1 is in its ‘OFF’ position but switch 2 is in its ‘ON’ position.
switch 1 is in its ‘ON’ position but switch 2 is in its ‘OFF’ position.
both switches 1 and 2 are in their ‘ON’ positions.
Answer – both switches 1 and 2 are in their ‘ON’ positions.
5. The relevant examples (2 each) have been correctly tabulated only in table-
Conductors – Silver Copper : Insulators – Bakelite Gold
Conductors -Gold Silver : Insulators – Bakelite Plastic
Conductors – Bakelite Copper : Insulators – Silver Plastic
Conductors – Gold Plastic : Insulators – Bakelite Copper
Answer – Conductors -Gold Silver : Insulators – Bakelite Plastic
D. Answers the following questions in brief.
1. State the function of the metallic strips used in a torch?
Answer – Metal strips in a torch act as the connecting wires. The flow of electric current is from the electric cell to the electric bulb through these connecting wires that heat the element of the bulb and the bulb lights up.
2. The given diagram shows a dry cell with its different parts marked as 1, 2, 3, 4 and 5. Which of them are the ‘two terminals’ of the dry cell?
Answer – 1- Metal cap(positive terminal)
5- Zinc case( negative terminal)
3. Write the meaning of the term ‘electric circuit’?
Answer – A complete and closed path through which an electric current can flow is called the electric circuit.
4. State the role of an electric switch in an electric circuit.
Answer – Electric switch helps us to start or stop the flow of current as of and when required.
5. Tools, like screw drivers and pliers, used by electricians, have handles made up of, (or covered with) plastic, rubber or wood. Why?
Answer – Plastic rubber or wood are bad conductors of electricity so electricians use the screwdrivers or pliers that have handles made up of them, so that they would not get an electric shock.
6. Why should we always dry our hands before touching an electric appliance, or a switch?
Answer – We should always dry our hands before touching an electric appliance because ordinary water is a good conductor of electricity and we may get an electric shock.
E. Answer the following questions.
1. Write in brief, the working of an electric torch.
Answer – When we slide or press the switch of the electric torch, electricity starts flowing from the electric cells to the electric bulb. This flow is through metallic strips which act as the connecting wires. This flow of electric current heats up the filament of the bulb. The bulb, therefore, lights up.
2. A student, while performing an experiment in the science laboratory, connected an electric bulb to an electric cell through an electric switch. He noticed that the bulb did not glow when the electric switch was set in its ON position. Mention ‘any two reasons’ for this observation.
Answer – Two possible reasons for the bulb to be not working may be:
(i)The bulb may be fused.
(ii) Cell may have dried out.
3. Separate out the devices, listed below, into categories that usually work with
(i) either batteries or mains (ii) batteries only (iii) mains only.
kettle, iron press, calculator, toaster, mobile phone, washing machine, radio, transistor, computer, microwave oven.
Answer – Either batteries or mains: Computer, transistor
Batteries only: Calculator, mobile phone, radio.
Mains only: Kettle, iron press, toaster, Microwave oven, washing machine.
4. Match the labels to the correct parts of the circuit given below. Will this circuit work? Justify your answer.
Answer –
No, this circuit will not work because the switch is in off position.
5. Distinguish between the terms conductors and insulators of electricity. Give two examples of each type.
Answer – Conductors: Materials, which allow electricity to pass through them easily, are called conductors. Examples – copper, silver
Value Based Question
The science teacher, on entering the class, observed that Ritika was looking quite upset. When she asked her the reason, Ritika told her that she had forgotten her raincoat in the bus. The teacher consoled her and advised her to be careful and particular about her belongings. She also told her not to get too upset and stay positive in her thoughts. She told her that positive thoughts light up our life in much the same way as an electric current lights up the bulb through which it flows.
1. Identify the values conveyed by the teacher to Ritika.
Answer – The values conveyed by the teacher to Ritika are positivity, carefulness.
2. How does an electric bulb ‘light up’ when an electric current flows through it?
Answer – When electric current passes through the electric bulb, it heats the filament and lights up.
3. Have a group-discussion in which one student states some situation/incident. Let the other students give their suggestions about dealing with that situation/ incident.
Answer – If one fails in any test and feels low, then other students can cheer him/her up and give him/her the motivation to work hard for the next test and get good marks.
Something To Do
1. Electric switches come in different sizes and shapes. Look around and list the different electrical devices/appliances in terms of their switches in a tabular form.
Answer – Appliances/Devices without switches – Mobile Phones, Wrist Watch
Appliances/Devices with Appliances/Devices with one switch – Table Lamp, Table Fan
more than one switch – Mixture, Grinder, Microwave oven
2. Open up a used up dry cell under the guidance of your teacher/parents. Observe each part carefully.
Answer – Students will do this task under the supervision of their elders.
3. Make a holder, for a battery of two cells, using a board and metallic strips. State the purpose served by the metallic strips in this set up.
Answer – Do it yourself
The metallic strips will serve as conducting wire between cells.
4. Select any five electric appliances/devices from your household and think of a plan for reducing their ‘electrical energy consumption. You can make a poster giving the details of your plan. Put it up on the class bulletin board to inspire, and motivate, the other students. Be ready to discuss their suggestions/ comments.
Answer – Do it yourself
5. Solve the following crossword puzzle with the help of the given clues.
Across →
3. An insulator – WOOD
5. A combination of two or more cells – BATTERY
6. A source of electricity – CELL
8. Path of the current – CIRCUIT
10. Allows current to pass – CONDUCTOR
Down↓
1. Does not allow current to pass – INSULATOR
2. Completes or break the circuit – SWITCH
4. An expensive and good conductor of electricity – SILVER
7. A source of light – BULB
9. Glows on heating – FILAMENT